Technique to reduce the third harmonic of an on-state RF switch

ABSTRACT

RF switching circuitry includes an RF switch coupled between an input node and an output node. Distortion compensation circuitry is coupled in parallel with the RF switch between the input node and the output node. The RF switch is configured to selectively pass an RF signal from the input node to the output node based on a first switching control signal. The distortion compensation circuitry is configured to boost a portion of the RF signal that is being compressed by the RF switch when the amplitude of the RF signal is above a predetermined threshold by selectively injecting current into one of the input node or the output node. Boosting a portion of the RF signal that is being compressed by the RF switch allows a signal passing through the RF switch to remain substantially linear, thereby improving the performance of the RF switching circuitry.

RELATED APPLICATIONS

This application claims the benefit of U.S. provisional patentapplication Ser. No. 61/820,319, filed May 7, 2013, the disclosure ofwhich is incorporated herein by reference in its entirety.

FIELD OF THE DISCLOSURE

The present disclosure relates to RF switching circuitry. Specifically,the present disclosure relates to RF switching circuitry includingdistortion compensation circuitry for cancelling harmonic distortiongenerated by one or more RF switching elements in the RF switchingcircuitry.

BACKGROUND

Modern mobile devices continue to demand increasing rates of dataexchange. One way to increase the rate of data exchange of a mobiledevice is by simultaneously transmitting and receiving radio frequency(RF) signals from a single antenna in the mobile device. Althougheffective at increasing the rate of data exchange that the mobile deviceis capable of achieving, the simultaneous use of a single antenna fortransmitting and receiving signals can result in interference betweentransmit and receive circuitry in the front end of the mobile device.The interference between the transmit and receive circuitry may beespecially problematic for certain combinations of transmit and receivefrequencies, such that the mobile device may become unusable in thesefrequency combinations.

FIG. 1 shows exemplary mobile device front end circuitry 10 fortransmitting and receiving RF signals from an antenna 12. The mobiledevice front end circuitry 10 includes a plurality of low band ports 14,a plurality of high band ports 16, a low band duplexer 18, a high bandduplexer 20, low band switching circuitry 22, high band switchingcircuitry 24, a diplexer 26, and antenna tuning circuitry 28. Theplurality of low band ports 14 are coupled to the low band switchingcircuitry 22 through the low band duplexer 18. Similarly, the pluralityof high band ports 16 are coupled to the high band switching circuitry24 through the high band duplexer 20. Both the low band switchingcircuitry 22 and the high band switching circuitry 24 are coupled to thediplexer 26, which is in turn coupled to the antenna 12 through theantenna tuning circuitry 28.

In a receive mode of operation, an RF signal is received at the antenna12, which is passed through the antenna tuning circuitry 28 to thediplexer 26, where it is separated into a low band signal component anda high band signal component. The low band signal component is deliveredto the low band switching circuitry 22, where it is then delivered to anappropriate one of the plurality of low band ports 14 through the lowband duplexer 18 so that it may be further processed by low band receivecircuitry (not shown). The high band signal component is delivered tothe high band switching circuitry 24, where it is then delivered to anappropriate one of the plurality of high band ports 16 through the highband duplexer 20 so that it may be further processed by high bandreceive circuitry (not shown).

In a transmit mode of operation, a transmit signal is provided to anappropriate one of the plurality of low band ports 14 or an appropriateone of the plurality of high band ports 16 from transmit circuitry (notshown). The transmit signal is passed through either the low bandswitching circuitry 22 or the high band switching circuitry 24 to thediplexer 26, where it is subsequently delivered to the antenna 12through the antenna tuning circuitry 28. As will be appreciated by thoseof ordinary skill in the art, the antenna tuning circuitry 28 mayinclude one or more RF switching elements for connecting variouscomponents to the antenna 12 in order to alter the impedance presentedto the antenna 12. The RF switching elements in the antenna tuningcircuitry 28 may be nonlinear, and therefore may generate harmonics ofsignals passed between the antenna 12 and the diplexer 26.

In certain combinations of transmit and receive frequencies, harmoniccomponents of a transmit signal may fall within the signal band of areceive signal. This may lead to harmonic distortion generated from thetransmit signal flowing back through the diplexer 26 and into thereceive circuitry. Because the transmit signal is generally a muchhigher amplitude signal than the receive circuitry is designed tohandle, the harmonic distortion may overpower and desensitize thereceive circuitry, thereby impeding the performance of the mobile devicefront end circuitry 10 or rendering it unusable altogether. For example,when transmitting in Band 17 (704-716 MHz), the third harmonic of thetransmit signal falls within a Band 4 receive signal (2110-2155 MHz).Accordingly, distortion about the third harmonic of Band 17 generateddue to the RF switching components in the antenna tuning circuitry 28will travel back through the diplexer 26 and into the Band 4 receivecircuitry, causing desensitization of the receive circuitry anddegrading the performance of the mobile device front end circuitry 10.

FIGS. 2A-2F show conventional RF switching circuitry 30 that may be usedin the antenna tuning circuitry 28 of FIG. 1 in a variety ofconfigurations. FIG. 2A shows conventional RF switching circuitry 30including a plurality of RF switching elements M_RF and adapted tooperate in a series configuration, wherein a signal presented at aninput node 32 is selectively passed to an output node 34 based on acontrol signal delivered to a control port 36. FIG. 2B showsconventional RF switching circuitry 30 adapted to operate in a seriesconfiguration, wherein the series equivalent of a first tuning capacitorC_TN1 and a second tuning capacitor C_TN2 is selectively presentedbetween an input node 32 and an output node 34 based on a control signaldelivered to a control port 36. FIG. 2C shows conventional RF switchingcircuitry 30 adapted to operate in a series configuration, wherein theseries equivalent of a first tuning inductor L_(—) TN1 and a secondtuning inductor L_TN2 is selectively presented between an input node 32and an output node 34 based on a control signal delivered to a controlport 36. FIG. 2D shows conventional RF switching circuitry 30 adapted tooperate in a shunt configuration, wherein a signal presented at an inputnode 32 is selectively shorted to ground. FIG. 2E shows conventional RFswitching circuitry 30 including a tuning capacitor C_TN and adapted tooperate in a shunt configuration, wherein a signal presented at an inputnode 32 is selectively shorted to ground through the tuning capacitorC_TN. FIG. 2F shows conventional RF switching circuitry 30 including atuning inductor L_TN and adapted to operate in a shunt configuration,wherein a signal presented at an input node 32 is selectively shorted toground through the tuning inductor L_TN. As will be appreciated by thoseof ordinary skill in the art, the antenna tuning circuitry 28 maycontain RF switching circuitry 30 in any of the previously mentionedconfigurations in order to alter the impedance presented to the antenna12.

As discussed above, while the RF switching circuitry 30 may allow tuningof the impedance presented to the antenna 12 in order to increase theefficiency of the mobile device front end circuitry 10, each one of theRF switching elements M_RF may generate harmonic distortion about apassing signal. The generated harmonic distortion may cause interferencebetween transmit and receive circuitry in the mobile device front endcircuitry 10, thereby degrading the performance of the circuitry.

Accordingly, there is a need for RF switching circuitry that is capableof passing RF signals while simultaneously reducing or eliminating thegeneration of harmonic distortion.

SUMMARY

RF switching circuitry includes an RF switch coupled between an inputnode and an output node. Distortion compensation circuitry is coupled inparallel with the RF switch between the input node and the output node.The RF switch is configured to selectively pass an RF signal from theinput node to the output node based on a first switching control signal.The distortion compensation circuitry is configured to boost a portionof the RF signal that is being compressed by the RF switch when theamplitude of the RF signal is above a predetermined threshold byselectively injecting current into one of the input node or the outputnode. Boosting a portion of the RF signal that is being compressed bythe RF switch allows a signal passing through the RF switch to remainsubstantially linear, thereby improving the performance of the RFswitching circuitry.

According to one embodiment, the distortion compensation circuitryincludes a compensation switch and an anti-parallel diode pair coupledin series with the compensation switch.

According to one embodiment, the compensation switch is closed duringthe ON state of the RF switching element and opened during an OFF stateof the RF switching element.

According to one embodiment, the anti-parallel diodes are coupled inseries between the first compensation switch and a second compensationswitch, such that the load seen at the input node and the output node isbalanced. A third compensation switch is coupled in parallel with theanti-parallel diodes. The first compensation switch and the secondcompensation switch are closed during the ON state of the RF switch andopened during an OFF state of the RF switch. The third compensationswitch is open during the ON state of the RF switch and closed during anOFF state of the RF switch.

According to one embodiment, the distortion compensation circuitry isisolated from the RF switch by one or more isolation capacitors. Theisolation capacitors enable the independent biasing of the RF switch andthe compensation circuitry, thereby allowing the independent operationof each.

Those skilled in the art will appreciate the scope of the disclosure andrealize additional aspects thereof after reading the following detaileddescription in association with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings incorporated in and forming a part of thisspecification illustrate several aspects of the disclosure, and togetherwith the description serve to explain the principles of the disclosure.

FIG. 1 shows a diagram illustrating conventional radio frequency frontend circuitry.

FIGS. 2A-2F show schematic representations of a plurality ofconventional RF switch configurations.

FIG. 3 shows a schematic representation of radio frequency switchingcircuitry including compensation circuitry according to one embodimentof the present disclosure.

FIG. 4 shows graph illustrating the operation of the radio frequencyswitching circuitry including compensation circuitry of FIG. 3 accordingto one embodiment of the present disclosure.

FIG. 5 shows a schematic representation of the radio frequency switchingcircuitry of FIG. 3 including details of the radio frequency switchingcircuitry according to one embodiment of the present disclosure.

FIG. 6 shows a schematic representation of radio frequency switchingcircuitry including compensation circuitry according to an additionalembodiment of the present disclosure.

FIG. 7 shows a schematic representation of the radio frequency switchingcircuitry of FIG. 6 including details of the radio frequency switchingcircuitry according to one embodiment of the present disclosure.

FIG. 8 shows a schematic representation of radio frequency switchingcircuitry including compensation circuitry according to an additionalembodiment of the present disclosure.

FIG. 9 shows a schematic representation of the radio frequency switchingcircuitry of FIG. 8 including details of the radio frequency switchingcircuitry according to one embodiment of the present disclosure.

FIG. 10 shows a schematic representation of radio frequency switchingcircuitry including compensation circuitry according to an additionalembodiment of the present disclosure.

FIG. 11 shows a schematic representation of the radio frequencyswitching circuitry shown in FIG. 10 including details of the radiofrequency switching circuitry according to one embodiment of the presentdisclosure.

FIG. 12 shows a graph illustrating the advantages of the radio frequencyswitching circuitry including compensation circuitry with respect toconventional radio frequency switching circuitry.

FIG. 13 shows a diagram illustrating a mobile terminal according to oneembodiment of the present disclosure.

DETAILED DESCRIPTION

The embodiments set forth below represent the necessary information toenable those skilled in the art to practice the disclosure andillustrate the best mode of practicing the disclosure. Upon reading thefollowing description in light of the accompanying drawings, thoseskilled in the art will understand the concepts of the disclosure andwill recognize applications of these concepts not particularly addressedherein. It should be understood that these concepts and applicationsfall within the scope of the disclosure and the accompanying claims.

It will be understood that, although the terms first, second, etc. maybe used herein to describe various elements, these elements should notbe limited by these terms. These terms are only used to distinguish oneelement from another. For example, a first element could be termed asecond element, and, similarly, a second element could be termed a firstelement, without departing from the scope of the present disclosure. Asused herein, the term “and/or” includes any and all combinations of oneor more of the associated listed items.

Relative terms such as “below” or “above” or “upper” or “lower” or“horizontal” or “vertical” may be used herein to describe a relationshipof one element, layer, or region to another element, layer, or region asillustrated in the Figures. It will be understood that these terms andthose discussed above are intended to encompass different orientationsof the device in addition to the orientation depicted in the Figures.

The terminology used herein is for the purpose of describing particularembodiments only and is not intended to be limiting of the disclosure.As used herein, the singular forms “a,” “an,” and “the” are intended toinclude the plural forms as well, unless the context clearly indicatesotherwise. It will be further understood that the terms “comprises,”“comprising,” “includes,” and/or “including” when used herein specifythe presence of stated features, integers, steps, operations, elements,and/or components, but do not preclude the presence or addition of oneor more other features, integers, steps, operations, elements,components, and/or groups thereof.

Unless otherwise defined, all terms (including technical and scientificterms) used herein have the same meaning as commonly understood by oneof ordinary skill in the art to which this disclosure belongs. It willbe further understood that terms used herein should be interpreted ashaving a meaning that is consistent with their meaning in the context ofthis specification and the relevant art and will not be interpreted inan idealized or overly formal sense unless expressly so defined herein.

Turning now to FIG. 3, RF switching circuitry 38 is shown according toone embodiment of the present disclosure. The RF switching circuitryincludes an RF switch SW_RF coupled in parallel with distortioncompensation circuitry 44 between an input node 40 and an output node42. The distortion compensation circuitry 44 includes a firstcompensation resistor R1, a second compensation resistor R2, a firstcompensation diode D1, a second compensation diode D2, and acompensation switch SW_C. The first compensation diode D1 and the secondcompensation diode D2 are coupled in an anti-parallel configurationbetween the first compensation resistor R1 and the second compensationresistor R2, such that the first compensation resistor R1, the pair ofanti-parallel compensation diodes D1 and D2, and the second compensationresistor R2 are coupled in series between the input node 40 and thecompensation switch SW_C. The compensation switch SW_C is coupledbetween the second compensation resistor R2 and the output node 42.Switch control circuitry 46 may be coupled to the RF switch SW_RF andthe compensation switch SW_C.

In operation, an RF signal RF_SIG is delivered to the input node 40 ofthe RF switching circuitry 38, where it is selectively forwarded via theRF switch SW_RF to the output node 42 based on a control signal providedto the RF switch SW_RF from the switch control circuitry 46. In the ONstate of the RF switching circuitry 38, both the RF switch SW_RF and thecompensation switch SW_C are closed. As will be appreciated by those ofordinary skill in the art, the RF switch SW_RF may have a non-lineargain response, which results in compression of the RF signal RF_SIG atthe output node 42 as the amplitude of the RF signal RF_SIG rises abovea given threshold. As discussed above, compression of the RF signalRF_SIG may result in distortion in the RF signal RF_SIG about one ormore harmonic frequencies. Accordingly, the distortion compensationcircuitry 44 is provided in order to prevent compression at the outputnode 42 as the amplitude of the RF signal RF_SIG increases.

Due to the internal resistance of the RF switch SW_RF, as current fromthe RF signal RF_SIG flows through the RF switch SW_RF, a differentialvoltage, defined as the difference between the voltage at the outputnode 42 and the voltage at the input node 40, is generated. As thedifferential voltage between the input node 40 and the output node 42rises above a threshold value, one of the first compensation diode D1 orthe second compensation diode D2 will become forward biased, therebyinjecting current into either the input node 40 or the output node 42,depending upon the polarity of the differential voltage, as discussed infurther detail below. Accordingly, a portion of the RF signal RF_SIG isboosted, thereby preventing compression of the RF signal RF_SIG at theoutput node 42.

In the OFF state of the RF switching circuitry 38, both the RF switchSW_RF and the compensation switch SW_C are open, thereby preventing theflow of current between the input node 40 and the output node 42.

FIG. 4 is a graph 48 illustrating the described functionality of the RFswitching circuitry 38 shown in FIG. 3. In a first section 50A of thegraph 48, a dotted line 52 represents the amount of current through thefirst compensation diode D1, while a solid line 54 represents the amountof current through the second compensation diode D2. In a second section50B of the graph 48, a solid line 56 represents the differential voltageacross the RF switch SW_RF. As shown by the graph 48, as thedifferential voltage rises above a certain positive threshold, such thatthe output node 42 is at a voltage higher than the input node 40 and thevoltage across the second compensation diode D2 exceeds the thresholdvoltage of the device, the second compensation diode D2 becomes forwardbiased, thereby allowing current to flow from the output node 42 to theinput node 40.

Similarly, as the differential voltage across the RF switch SW_RF fallsbelow a certain negative threshold, such that the voltage at the inputnode 40 is higher than the voltage at the output node 42 and the voltageacross the first compensation diode D1 exceeds the threshold voltage ofthe device, the first compensation diode D1 becomes forward biased,thereby allowing current to flow from the input node 40 to the outputnode 42.

FIG. 5 shows details of the RF switching circuitry 38 shown in FIG. 3.As shown in FIG. 5, the RF switch SW_RF may comprise a plurality of RFswitching elements M_RF coupled in series between the input node 40 andthe output node 42. The RF switching elements M_RF may be transistordevices such as metal-oxide-semiconductor field-effect transistors(MOSFETs), field-effect transistors (FETs), or the like. Accordingly,the source and drain contacts of each one of the RF switching elementsM_RF may be coupled in series as shown, while the gate contacts of eachone of the RF switching elements M_RF may be coupled together to form acontrol port for the RF switch SW_RF, which may be coupled to the switchcontrol circuitry 46. As will be appreciated by those of ordinary skillin the art, providing the plurality of RF switching elements M_RFcoupled in series allows the RF switch SW_RF to handle larger amplitudesignals without damage to the device.

Similar to the RF switch SW_RF, the compensation switch SW_C may alsocomprise a plurality of compensation switching elements M_C coupled inseries between the second compensation resistor R2 and the output node42. The compensation switching elements M_C may be transistor devicessuch as MOSFETs, FETs, or the like. Accordingly, the source and draincontacts of each one of the compensation switching elements M_C may becoupled in series as shown, while the gate contacts of each one of thecompensation switching elements M_C may be coupled together to form acontrol port for the compensation switch SW_C, which may be coupled tothe switch control circuitry 46. As will be appreciated by those ofordinary skill in the art, providing the plurality of compensationswitching elements M_C coupled in series allows the compensation switchSW_C to handle larger amplitude signals without damage to the device.

Additionally, the first compensation diode D1 may be a firstdiode-connected transistor M_D1, and the second compensation diode D2may be a second diode-connected transistor M_D2. Specifically, the gatecontact of each one of the first diode-connected transistor M_D1 and thesecond diode-connected transistor M_D2 may be coupled to the draincontact of the first diode-connected transistor M_D1 and the seconddiode connected transistor M_D2, respectively. Further, the body contactof each one of the first diode-connected transistor M_D1 and the seconddiode-connected transistor M_D2 may be connected to the drain contact ofthe first diode-connected transistor M_D1 and the second diode-connectedtransistor M_D2, respectively. Finally, the source contact of the seconddiode-connected transistor M_D2 may be coupled to the drain contact ofthe first diode-connected transistor M_D1, and the source contact of thefirst diode-connected transistor M_D1 may be coupled to the draincontact of the second diode-connected transistor M_D2.

FIG. 6 shows the RF switching circuitry 38 according to an additionalembodiment of the present disclosure. The RF switching circuitry 38shown in FIG. 6 is substantially similar to that shown in FIG. 3, butfurther includes two additional compensation switches, such that the RFswitching circuitry 38 includes a first compensation switch SW_C1, asecond compensation switch SW_C2, and a third compensation switch SW_C3.The first compensation switch SW_C1 is coupled between the input node 40and the first compensation resistor R1. The second compensation switchSW_C2 is coupled between the second compensation resistor R2 and theoutput node 42. The third compensation switch SW_C3 is coupled inparallel with the first compensation diode D1 and the secondcompensation diode D2. Notably, while the RF switch SW_RF, the firstcompensation switch SW_C1, and the second compensation switch SW_C2 areclosed, the third compensation switch SW_C3 is open, and vice-versa. Byarranging the compensation switches in this manner, the same load ispresented to both the input node 40 and the output node 42, making theRF switching circuitry 38 more suitable for series switchingapplications. Further, providing the third compensation switch SW_C3prevents the first compensation diode D1 and the second compensationdiode D2 from conducting current when the RF switching circuitry 38 isin an OFF state of operation.

FIG. 7 shows details of the RF switching circuitry 38 shown in FIG. 6.As discussed above, the RF switch SW_RF may comprise a plurality ofseries-coupled RF switching elements M_RF. Additionally, the firstcompensation switch SW_C1 and the second compensation switch SW_C2 maycomprise a plurality of series-coupled compensation switching elementsM_C. Further, the first compensation diode D1 and the secondcompensation diode D2 may comprise a first diode-connected transistorM_D1 and a second diode-connected transistor M_D2, respectively.Finally, the third compensation switch SW_C3 may comprise acomplementary compensation switching element M_CC, such that thecomplementary compensation switching element M_CC remains closed whenthe first compensation switch SW_C1, the second compensation switchSW_C2, and the RF switch SW_RF are open, and vice versa. Accordingly,the complementary compensation switching element M_CC may be a PMOStransistor, while the RF switching elements M_RF and the compensationswitching elements M_C may be NMOS transistors.

FIG. 8 shows the RF switching circuitry 38 according to an additionalembodiment of the present disclosure. The RF switching circuitry 38shown in FIG. 8 is substantially similar to that shown in FIG. 7, butfurther includes a first compensation capacitor C1 and a secondcompensation capacitor C2. The first compensation capacitor C1 iscoupled between the input node 40 and the first compensation switchSW_C1. The second compensation capacitor C2 is coupled between thesecond compensation switch SW_C2 and the output node 42. The firstcompensation capacitor C1 and the second compensation capacitor C2 allowa DC bias voltage to be applied across the distortion compensationcircuitry 44 without affecting the RF signal RF_SIG. Accordingly, thefirst compensation switch SW_C1, the second compensation switch SW_C2,and the third compensation switch SW_C3 may be controlled independentlyfrom the RF switch SW_RF, thereby allowing for greater flexibility inthe operation of the RF switching circuitry 38. For example, thedistortion compensation circuitry 44 may be disabled independently ofthe RF switch SW_RF at very high or very low power levels where thecompensation technique may not be helpful.

FIG. 9 shows details of the RF switching circuitry 38 shown in FIG. 8.As discussed above, the RF switch SW_RF may comprise a plurality ofseries-coupled RF switching elements M_RF. Additionally, the firstcompensation switch SW_C1 and the second compensation switch SW_C2 maycomprise a plurality of series-coupled compensation switching elementsM_C. Further, the first compensation diode D1 and the secondcompensation diode D2 may comprise a first diode-connected transistorM_D1 and a second diode-connected transistor M_D2, respectively.Finally, the third compensation switch SW_C3 may comprise acomplementary compensation switching element M_CC, such that thecomplementary compensation switching element M_CC remains closed whenthe first compensation switch SW_C1, the second compensation switchSW_C2, and the RF switch SW_RF are open, and vice versa. Accordingly,the complementary compensation switching element M_CC may be a PMOStransistor, while the RF switching elements M_RF and the compensationswitching elements M_C may be NMOS transistors.

FIG. 10 shows the RF switching circuitry 38 according to an additionalembodiment of the present disclosure. The RF switching circuitry 38shown in FIG. 10 is substantially similar to that shown in FIG. 8, butfurther includes a third compensation capacitor C3 and a fourthcompensation capacitor C4, as well as compensation bias circuitry 58.The third compensation capacitor C3 is coupled in series between thefirst compensation resistor R1 and the anode of the first compensationdiode D1. The fourth compensation capacitor C4 is coupled between thesecond compensation resistor R2 and the anode of the second compensationcapacitor D2. The compensation bias circuitry 58 is coupled at the anodeof each one of the first compensation diode D1 and the secondcompensation diode D2. Including the third compensation capacitor C3 andthe fourth compensation capacitor C4 allows a DC bias voltage to beapplied to the anode of each one of the first compensation diode D1 andthe second compensation diode D2 without affecting the operation of thedistortion compensation circuitry 44.

By applying a DC voltage to the anode of each one of the firstcompensation diode D1 and the second compensation diode D2, the voltageat the first compensation diode D1 and the second compensation diode D2can be altered in order to change when each one of the diodes willbecome forward biased. Accordingly, the compensation bias circuitry 58can control when the first compensation diode D1 and the secondcompensation diode D2 activate to control how much compensation isapplied to the RF switching circuitry 38. For example, if a positive DCvoltage is applied to the anode of the first compensation diode D1 andthe second compensation diode D2, the threshold voltage of each one ofthe diodes will effectively be lowered. Accordingly, each one of thefirst compensation diode D1 and the second compensation diode D2 willbecome forward biased at a smaller differential voltage across the RFswitch SW_RF, which will result in more compensation for distortion inthe RF switching circuitry 38. As another example, if a negative DCvoltage is applied to the anode of the first compensation diode D1 andthe second compensation diode D2, the threshold voltage of each one ofthe diodes will effectively be heightened. Accordingly, each one of thefirst compensation diode D1 and the second compensation diode D2 willbecome forward biased at a larger differential voltage across the RFswitch SW_RF, which will result in less compensation for distortion inthe RF switching circuitry 38.

The compensation bias circuitry 58 may comprise, for example, a DCvoltage source, an operational amplifier, a digital to analog converter,or a digital to analog converter with a temperature dependent reference.Those of ordinary skill in the art will appreciate that the compensationbias circuitry 58 may comprise any circuitry capable of applying acontrolled DC voltage without departing from the principles of thepresent disclosure.

FIG. 11 shows details of the RF switching circuitry 38 shown in FIG. 10.As discussed above, the RF switch SW_RF may comprise a plurality ofseries-coupled RF switching elements M_RF. Additionally, the firstcompensation switch SW_C1 and the second compensation switch SW_C2 maycomprise a plurality of series-coupled compensation switching elementsM_C. Further, the first compensation diode D1 and the secondcompensation diode D2 may comprise a first diode-connected transistorM_D1 and a second diode-connected transistor M_D2, respectively.Finally, the third compensation switch SW_C3 may comprise acomplementary compensation switching element M_CC, such that thecomplementary compensation switching element M_CC remains closed whenthe first compensation switch SW_C1, the second compensation switchSW_C2, and the RF switch SW_RF are open, and vice versa. Accordingly,the complementary compensation switching element M_CC may be a PMOStransistor, while the RF switching elements M_RF and the compensationswitching elements M_C may be NMOS transistors.

Any of the RF switching circuitry 38 described above with respect toFIGS. 3 and 5-11 may replace conventional RF switching circuitry togenerate performance improvements in an RF device in which the RFswitching circuitry 38 is incorporated. For example, the RF switchingcircuitry 38 described above may replace the conventional RF switchingcircuitry in any of the configurations described above in FIGS. 2A-2F toprovide improved series RF switches, shunt RF switches, or RF tuningswitches of any kind.

FIG. 12 is a graph 60 depicting the harmonic power vs. the fundamentalpower of the RF switching circuitry with and without the distortioncompensation circuitry 44. The dotted line 62 in FIG. 12 shows the thirdharmonic response of the RF switching circuitry 38 without thedistortion compensation circuitry 44, while a solid line 64 in FIG. 12shows the third harmonic response of the RF switching circuitry 38 withthe distortion compensation circuitry 44. As shown in FIG. 12, there isa marked decrease in the third harmonic response of the RF switchingcircuitry 38 when the distortion compensation circuitry 44 is active.Accordingly, the performance of the RF switching circuitry 38 may besubstantially improved.

One application of the RF switching circuitry 38 shown in FIGS. 3, 5, 6,7, 8, 9, 10, and 11 is in the antenna tuning circuitry used in a mobileterminal 66, the basic architecture of which is represented in FIG. 13.The mobile terminal 66 may include a receiver front end 68, a radiofrequency transmitter section 70, an antenna 72, antenna tuningcircuitry 74, a duplexer or switch 76, a baseband processor 78, acontrol system 80, a frequency synthesizer 82, and an interface 84. Thereceiver front end 68 receives information bearing radio frequencysignals from one or more remote transmitters provided by a base station(not shown). The radio frequency signal is passed through the antennatuning circuitry 74, which may include the RF switching circuitry 38 forswitching one or more components into contact with the antenna 72 inorder to alter the response of the antenna 72. A low noise amplifier(LNA) 86 amplifies the signal. Filtering circuitry 88 minimizesbroadband interference in the received signal, while down conversion anddigitization circuitry 90 down converts the filtered, received signal toan intermediate or baseband frequency signal, which is then digitizedinto one or more digital streams. The receiver front end 68 typicallyuses one or more mixing frequencies generated by the frequencysynthesizer 82. The baseband processor 78 processes the digitizedreceived signal to extract the information or data bits conveyed in thesignal. This processing typically comprises demodulation, decoding, anderror correction operations. As such, the baseband processor 78 istypically implemented in one or more digital signal processors (DSPs).

On the transmit side, the baseband processor 78 receives digitized data,which may represent voice, data, or control information, from thecontrol system 80, which it encodes for transmission. The encoded datais output to the radio frequency transmitter section 70, where it isused by a modulator 92 to modulate a carrier signal at a desiredtransmit frequency. An RF power amplifier 94 amplifies the modulatedcarrier signal to a level appropriate for transmission, and delivers theamplified and modulated carrier signal to the antenna 72 through theduplexer or switch 76 and the antenna tuning circuitry 74.

A user may interact with the mobile terminal 66 via the interface 84,which may include interface circuitry 96 associated with a microphone98, a speaker 100, a keypad 102, and a display 104. The interfacecircuitry 96 typically includes analog-to-digital converters,digital-to-analog converters, amplifiers, and the like. Additionally, itmay include a voice encoder/decoder, in which case it may communicatedirectly with the baseband processor 78. Audio information encoded inthe received signal is recovered by the baseband processor 78, andconverted by the interface circuitry 96 into an analog signal suitablefor driving the speaker 100. The keypad 102 and the display 104 enablethe user to interact with the mobile terminal 66. For example, thekeypad 102 and the display 104 may enable the user to input numbers tobe dialed, access address book information, or the like, as well asmonitor call progress information.

Those skilled in the art will recognize improvements and modificationsto the embodiments of the present disclosure. All such improvements andmodifications are considered within the scope of the concepts disclosedherein and the claims that follow.

What is claimed is:
 1. Circuitry comprising: a radio frequency (RF)switch coupled between an input node and an output node and configuredto selectively pass an RF signal from the input node to the output nodebased on a first switching control signal; and distortion compensationcircuitry coupled in parallel with the RF switch between the input nodeand the output node, the distortion compensation circuitry configured toboost a portion of the RF signal that is being compressed by the RFswitch when the amplitude of the RF signal is above a predeterminedthreshold by selectively injecting current into one of the input node orthe output node.
 2. The circuitry of claim 1 wherein the distortioncompensation circuitry comprises: a compensation switch; and a firstcompensation diode coupled in an anti-parallel configuration with asecond compensation diode to form an anti-parallel diode pair, such thatthe anti-parallel diode pair is coupled in series with the compensationswitch between the input node and the output node.
 3. The circuitry ofclaim 2 wherein the distortion compensation circuitry further comprises:a first compensation resistor coupled between the input node and theanti-parallel diode pair; and a second compensation resistor coupledbetween the anti-parallel diode pair and the compensation switch.
 4. Thecircuitry of claim 2 wherein the compensation switch is controlled by asecond switching control signal, such that when the RF switch is closed,the compensation switch is also closed, and when the RF switch is open,the compensation switch is also open.
 5. The circuitry of claim 4further comprising switching control circuitry configured to deliver thefirst switching control signal to the RF switch and the second switchingcontrol signal to the compensation switch.
 6. The circuitry of claim 1wherein the distortion compensation circuitry comprises: a firstcompensation diode coupled in an anti-parallel configuration with asecond compensation diode to form an anti-parallel diode pair; a firstcompensation switch coupled between the input node and the anti-paralleldiode pair; a second compensation switch coupled between the output nodeand the anti-parallel diode pair; and a third compensation switchcoupled in parallel with the first compensation diode and the secondcompensation diode.
 7. The circuitry of claim 6 wherein the distortioncompensation circuitry further comprises: a first compensation resistorcoupled between the first compensation switch and the anti-paralleldiode pair; and a second compensation resistor coupled between thesecond compensation switch and the anti-parallel diode pair.
 8. Thecircuitry of claim 7 further comprising: a first compensation capacitorcoupled between the input node and the first compensation switch; and asecond compensation capacitor coupled between the output node and thesecond compensation switch.
 9. The circuitry of claim 8 wherein thefirst compensation switch, the second compensation switch, and the thirdcompensation switch are controlled independently of the RF switch. 10.The circuitry of claim 8 further comprising: a third compensationcapacitor coupled between an anode of the first compensation diode andthe first compensation resistor; and a fourth compensation capacitorcoupled between an anode of the second compensation diode and the secondcompensation resistor.
 11. The circuitry of claim 10 further comprisingcompensation bias circuitry configured to provide a biasing voltage tothe anode of the first compensation diode and the second compensationdiode.
 12. The circuitry of claim 6 wherein the first compensationswitch and the second compensation switch comprise one or more NMOStransistors, and the third compensation switch comprises one or morePMOS transistors.
 13. The circuitry of claim 12 wherein the firstcompensation switch, the second compensation switch, and the thirdcompensation switch are controlled by a second switching control signal,such that when the RF switch is closed, the first compensation switchand the second compensation switch are also closed, while the thirdcompensation switch is open, and when the RF switch is open, the firstcompensation switch and the second compensation switch are also open,while the third compensation switch is closed.
 14. The circuitry ofclaim 13 further comprising switching control circuitry configured todeliver the first switching control signal to the RF switch and thesecond switching control signal to the first compensation switch, thesecond compensation switch, and the third compensation switch.
 15. Thecircuitry of claim 1 wherein the distortion compensation circuitry isconfigured to boost a portion of the RF signal that is being compressedby the RF switch when the amplitude of the RF signal is above apredetermined threshold by selectively injecting current into the inputnode.
 16. The circuitry of claim 1 wherein the distortion compensationcircuitry is configured to boost a portion of the RF signal that isbeing compressed by the RF switch when the amplitude of the RF signal isabove a predetermined threshold by selectively injecting current intothe output node.
 17. A mobile terminal comprising: an antenna; areceiver front end; a radio frequency transmitter section; and antennatuning circuitry coupled between the antenna, the receiver front end,and the radio frequency transmitter section, the antenna tuningcircuitry comprising: a radio frequency (RF) switch coupled between aninput node and an output node and configured to selectively pass an RFsignal from the input node to the output node based on a first switchingcontrol signal; and distortion compensation circuitry coupled inparallel with the RF switch between the input node and the output node,the distortion compensation circuitry configured to boost a portion ofthe RF signal that is being compressed by the RF switch when theamplitude of the RF signal is above a predetermined threshold byselectively injecting current into one of the input node or the outputnode.
 18. The mobile terminal of claim 17 wherein the output node of theantenna tuning circuitry is coupled to a fixed impedance.
 19. The mobileterminal of claim 18 wherein the antenna tuning circuitry is configuredto alter the impedance presented to the antenna by selectively closingthe RF switch.
 20. The mobile terminal of claim 17 wherein thedistortion compensation circuitry comprises: a compensation switch; anda first compensation diode coupled in an anti-parallel configurationwith a second compensation diode to form an anti-parallel diode pair,such that the anti-parallel diode pair is coupled in series with thecompensation switch between the input node and the output node.
 21. Themobile terminal of claim 20 wherein the distortion compensationcircuitry further comprises: a first compensation resistor coupledbetween the input node and the anti-parallel diode pair; and a secondcompensation resistor coupled between the anti-parallel diode pair andthe compensation switch.
 22. The mobile terminal of claim 20 wherein thecompensation switch is controlled by a second switching control signal,such that when the RF switch is closed, the compensation switch is alsoclosed, and when the RF switch is open, the compensation switch is alsoopen.
 23. The mobile terminal of claim 17 wherein the distortioncompensation circuitry comprises: a first compensation diode coupled inan anti-parallel configuration with a second compensation diode to forman anti-parallel diode pair; a first compensation switch coupled betweenthe input node and the anti-parallel diode pair; a second compensationswitch coupled between the output node and the anti-parallel diode pair;and a third compensation switch coupled in parallel with the firstcompensation diode and the second compensation diode.
 24. The mobileterminal of claim 23 wherein the distortion compensation circuitryfurther comprises: a first compensation resistor coupled between thefirst compensation switch and the anti-parallel diode pair; and a secondcompensation resistor coupled between the second compensation switch andthe anti-parallel diode pair.
 25. The mobile terminal of claim 24wherein the distortion compensation circuitry further comprises: a firstcompensation capacitor coupled between the input node and the firstcompensation switch; and a second compensation capacitor coupled betweenthe output node and the second compensation switch.
 26. The mobileterminal of claim 25 wherein the first compensation switch, the secondcompensation switch, and the third compensation switch are controlledindependently of the RF switch.
 27. The mobile terminal of claim 25wherein the distortion compensation circuitry further comprises: a thirdcompensation capacitor coupled between an anode of the firstcompensation diode and the first compensation resistor; and a fourthcompensation capacitor coupled between an anode of the secondcompensation diode and the second compensation resistor.
 28. The mobileterminal of claim 27 wherein the distortion compensation circuitryfurther comprises compensation bias circuitry configured to provide abiasing voltage to the anode of the first compensation diode and thesecond compensation diode.
 29. The mobile terminal of claim 23 whereinthe first compensation switch and the second compensation switchcomprise one or more NMOS transistors, and the third compensation switchcomprises one or more PMOS transistors.
 30. The mobile terminal of claim29 wherein the first compensation switch, the second compensationswitch, and the third compensation switch are controlled by a secondswitching control signal, such that when the RF switch is closed, thefirst compensation switch and the second compensation switch are alsoclosed, while the third compensation switch is open, and when the RFswitch is open, the first compensation switch and the secondcompensation switch are also open, while the third compensation switchis closed.
 31. The mobile terminal of claim 30 further comprisingswitching control circuitry configured to deliver the first switchingcontrol signal to the RF switch and the second switching control signalto the first compensation switch, the second compensation switch, andthe third compensation switch.
 32. The circuitry of claim 17 wherein thedistortion compensation circuitry is configured to boost a portion ofthe RF signal that is being compressed by the RF switch when theamplitude of the RF signal is above a predetermined threshold byselectively injecting current into the input node.
 33. The circuitry ofclaim 17 wherein the distortion compensation circuitry is configured toboost a portion of the RF signal that is being compressed by the RFswitch when the amplitude of the RF signal is above a predeterminedthreshold by selectively injecting current into the output node.